1. Field of the Invention
This invention relates to the field of ac POWER CONTROL and in particular to the field of thyristor drive circuits.
2. Prior Art
A thyristor-drive circuit is shown in FIG. 5 of U.S. Pat. No. 4,174,496, issued Nov. 13, 1979 and titled MONOLITHIC SOLID STATE POWER CONTROLLER, assigned to the common assignee. This circuit is relevant for its use of junction field effect transistors coupled between the respective gates and cathodes of anti-parallel silicon controlled rectifiers (SCRs) and the use of an isolation transformer. It does not show the use of an N-channel insulated gate field effect transistors, and a blocking diodes coupled in series between the respective anodes and gates of the SCRs. A variety of triggering circuits are characterized in texts such as the "GE Transistor Manual", published by General Electric in 1964. A number of manufacturers' application literature publications are available on the subject of SCR and thyristor power control circuits directly from manufacturers such as Motorola, P.O. Box 20924, Phoenix, Ariz. 85036, the RCA Company at Summerville, N.J., and TECCOR INC at P.O. Box 61447, Dallas, Tex. 75261.
The thyristor drive circuits taught by the above references are typically concerned with the thyristor control of circuits powered from a 60 Hz voltage source. Drive circuits of conventional design typically consume power from a low voltage dc voltage source such as a 5 or 10 V. power supply. Many applications, requiring the use of large numbers of thyristors drive circuits do not have a low voltage auxiliary power source available. Thyristor drive circuits typically require the use of an auxiliary low voltage source comprising a step-down isolation transformer and a rectifier filter power supply to generate the auxiliary low voltage source to power the thyristor drive circuit. A low voltage power source of this type has weight, volume and cost not present in the invention circuit.